gno/usr.man/man3/directory.3

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.TH DIRECTORY 3 "29 January 1997" GNO "Library Routines"
.SH NAME
.BR opendir ,
.BR readdir ,
.BR telldir ,
.BR seekdir ,
.BR rewinddir ,
.BR closedir ,
.BR dirfd
\- directory operations
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <dirent.h>

DIR *\fBopendir\fR (const char *\fIfilename\fR);
struct \fBdirent\fR *readdir (DIR *\fIdirp\fR);
long \fBtelldir\fR (const DIR *\fIdirp\fR);
void \fBseekdir\fR (DIR *\fIdirp\fR, long \fIloc\fR);
void \fBrewinddir\fR (DIR *\fIdirp\fR);
int \fBclosedir\fR (DIR *\fIdirp\fR);
int \fBdirfd\fR (DIR *\fIdirp\fR);
.fi
.SH DESCRIPTION
The
.BR opendir 
function
opens the directory named by
.IR filename ,
associates a
.IR "directory stream"
with it
and
returns a pointer to be used to identify the
.IR "directory stream"
in subsequent operations.  The pointer
.BR NULL
is returned if
.I filename
cannot be accessed, or if it cannot
.BR malloc (3)
enough memory to hold the whole thing.
.LP
The
.BR readdir 
function
returns a pointer to the next directory entry.  It returns
.BR NULL
upon reaching the end of the directory or detecting an invalid
.BR seekdir 
operation.
The GNO implementation will not return entries for either the current
directory
.RB ( . )
or the parent directory
.RB ( .. ).
Directory entries are defined by the following structure in <sys/dirent.h>:
.nf

struct dirent {
	unsigned long	d_fileno;	/* file number of entry */
	unsigned short	d_reclen;	/* length of this record */
	unsigned char	d_type;		/* file type (non-IIgs) */
	unsigned char	d_namlen;	/* length of string in d_name */
	char		d_name[256];	/* name must be no longer than this */
}

.fi
The value of
.BR d_fileno
is, on most architectures, the inode of the current file.  Since inodes
are not used on any current GS/OS FSTs, this number corresponds to the
offset of this file in the current directory.
.BR d_reclen
is the length of the entire struct dirent.
The
.BR d_type
member is currently set to 
.BR DT_DIR
for directories, 
.BR DT_REG
otherwise.
.BR d_namlen
is the length of the file name contained in
.BR d_name .
.LP
Subsequent calls to 
.BR readdir 
will overwrite previous results in the struct dirent; if the results
must be saved then they should be 
.BR memcpy \'d
to a user-defined buffer.
.LP
The
.BR telldir 
function
returns the current location associated with the named
.IR "directory stream" .
The result of a
.BR telldir
on a stream which has just been opened is undefined.
.LP
The
.BR seekdir 
function
sets the position of the next
.BR readdir 
operation on the
.IR "directory stream" .
The new position reverts to the one associated with the
.IR "directory stream"
when the
.BR telldir 
operation was performed.  Values returned by
.BR telldir 
are good only for the lifetime of the
.BR DIR
pointer,
.RI ( dirp )
from which they are derived.
If the directory is closed and then reopened, the 
.BR telldir 
value may be invalidated due to undetected directory compaction.
.LP
The
.BR rewinddir 
function
resets the position of the named
.IR "directory stream"
to the beginning of the directory.
.LP
The
.BR closedir 
function
closes the named
.IR "directory stream"
and frees the structure associated with the
.I dirp
pointer,
returning 0 on success.
On failure, \-1 is returned and the global variable
.IR errno
is set to indicate the error.
.LP
The
.BR dirfd 
function
returns the integer file descriptor associated with the named
.IR "directory stream" ,
see
.BR open (2).
.SH EXAMPLE
Sample code which searches a directory for entry ``name'' in a
case-sensitive manner is:
.nf

len = strlen(name);
dirp = opendir(".");
while ((dp = readdir(dirp)) != NULL)
	if (dp->d_namlen == len && !strcmp(dp->d_name, name)) {
		(void)closedir(dirp);
		return FOUND;
	}
(void)closedir(dirp);
return NOT_FOUND;
.fi
.SH BUGS
The GNO implementation of 
.BR seekdir
and
.BR rewinddir
rely on the GS/OS call
.BR GetDirEntryGS .
It is thus possible for these routines to fail.  If they do, the error
will not be detected until a subsequent
.BR readdir 
is performed.
.SH SEE ALSO
.BR open (2),
.BR close (2),
.BR read (2),
.BR lseek (2),
.BR dir (5)
.SH HISTORY
The
.BR opendir ,
.BR readdir ,
.BR telldir ,
.BR seekdir ,
.BR rewinddir ,
.BR closedir ,
and
.BR dirfd 
functions appeared in
BSD 4.2.